HARRISBURG (TNS) — Last month, The Atlantic featured a big spread on Democratic Lt. Gov. John Fetterman’s effort to win a U.S. Senate seat in 2022.

Last week, NBC News called the race for that seat “a test of progressive firepower” in a swing state in the wake of Donald Trump.

This past Monday, a fourth Democrat joined the race. On Tuesday, a fourth Republican announced. It’s expected there will be larger candidate fields in primaries more than a year from now.

Campaigns start too early, last too long. But growing attention to this one’s understandable. It’s different. Huge for the state, and maybe the nation.

First, it could decide Senate control.

Right now, the Senate is 50-50, but operationally Democratic since Vice President Kamala Harris’ role as Senate president includes the clout of a tie-breaking vote.

Second, it’s an open-seat race, rare in Pennsylvania. We’ve had only three in the last half-century: 1976, after Republican Hugh Scott decided to retire; 1980, after Republican Richard Schweiker announced he wouldn’t seek reelection; and 1991, a special election following the death of Republican John Heinz.

(Purists argue 2010 was an open-seat because incumbent Republican Arlen Specter switched parties and then lost in the Democratic primary. I don’t see it that way. Discuss among yourselves.)

Ours, as of now, is one of five open-seat Senate races nationally. All five are held by Republicans: Alabama, Missouri, North Carolina, Ohio and here. All but one is seen as likely, leaning or safe for the GOP. That one is Pennsylvania.

Our seat is rated a “toss up” by University of Virginia national prognosticator Larry Sabato. And pegged by CNN as most likely to flip in 2022.

That doesn’t mean Sen. Pat Toomey’s leaving is an outright gift to Democrats. It means a bruising battle with both sides backed by mountains of money, during, as usual in mid-term elections, a referendum on the president and his party.

“There will be a tremendous amount of money raised and spent,” says Berwood Yost, director of Franklin & Marshall College’s Center for Opinion Research. “The money spent will be focused on the candidates and perceptions of the president’s performance. I’m willing to bet we hear as much about Joe Biden as we hear about whoever is running.”

J.J. Balaban, a Philly-based Democratic ad-maker, has worked on campaigns across the country. He says an open-seat race is “absolutely” different than a race with an incumbent.

“Typically, it’s harder to defeat an incumbent than win an open seat,” he says, adding, “There’s a very long tradition of incumbents using their positions to get known … in a mega-state like Pennsylvania it’s very hard to get known.”

This presents enormous challenges to almost everyone announced to date.

Fetterman is better known than others. He’s run statewide before: Senate in 2016, lieutenant governor in 2018. And he raised $4 million so far this year.

(For perspective, Toomey raised and spent $30 million to win in 2016.)

Still, an F&M poll last month shows 44% of state voters don’t know enough about Fetterman to have an opinion and just 29% view him strongly or somewhat favorably.

Other announced Democrats include Philly state Rep. Malcolm Kenyatta, businessman and former Norristown Council President John McGuigan, and physician and Montgomery County Commissioner Valerie Arkoosh, who formally jumped in last Monday. More are expected.

Republicans include Montgomery County developer and 2018 Lt. Gov. candidate Jeff Bartos, Chester County businessman Everett Stern, Montgomery County attorney Sean Gale and Montgomery County conservative commentator and 2020 congressional candidate Kathy Barnette, who announced this past Tuesday. More are expected.

In fact, as other possible candidates — current and former members of Congress and those who’ve run statewide in the past — decide if they’re in or out, the race and its runners will get notice over and over again.

Plus, both parties, their voters and candidates will make news answering (or wrestling with) questions about how far right or how far left nominees should be.

Democrats hope Biden administration steps to beat back the pandemic and pump up the economy nullify normal mid-term backlash against the party in power.

Republicans hope to sell a message that political balance in governing is better than a Democratic monopoly.

Predicting how it turns out is like seeking to stop telemarketers with a government no-call list — useless.

Buying into early projections of a Pennsylvania race certain to be nationalized, without knowing the state of the nation a year from now, is risky.

But one thing’s for sure. The race will draw tons of attention. And that’s good for democracy.

(John Baer is a columnist for The Patriot-News of Harrisburg.)